[Sema] Report unused newValue when getter is accessed by member reference

[KingOfBrian]

This PR fixes a missed scenario in an earlier fix for SR-964 which warns if a getter is accessed when the newValue parameter of a setter is not used. The previous fix, disappointingly misses the case of variables inside of classes or structs and only works on global variables. I experienced a bit of unit-test tunnel vision, and didn't test the scenario I was hoping to fix 😬.

I made this PR against 4.1 in hopes that it could land in the next release, even though I'm guessing it is a bit of a long shot!

Really ™️ Resolves SR-964.

[milseman]

Much of this is pretty old code. @lattner or @xedin, do you think you can review this change? Do you think this is important enough to nominate for Swift-4.1?

[milseman]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 63519a3

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 63519a3

[milseman]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 63519a3

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 63519a3

[tkremenek]

This change should be proposed on master first before being pulled into a release branch. Release branches do not forward to master.

Please propose this change on master first! Thank you.

[tkremenek]

@KingOfBrian sorry for not re-directing sooner. I may be mistaken but this does not look already on master. Please create a new PR against master to review the change there. It is very late to take this change for 4.1, but this looks promising!